Document max CSI parameter count

src/input_common.rs

@@ -806,6 +806,7 @@ fn parse_codepoint(
 
     fn parse_csi(&mut self, buffer: &mut Vec<u8>) -> Option<Key> {
         let mut next_char = |zelf: &mut Self| zelf.try_readb(buffer).unwrap_or(0xff);
+        // The maximum number of CSI parameters is defined by NPAR, nominally 16.
         let mut params = [[0_u32; 4]; 16];
         let mut c = next_char(self);
         let private_mode;